The performance of data storage systems typically depends in part on the arrangement or configuration of the stored data. For example, data items that are heavily utilized are often distributed among multiple storage devices in the system to avoid “bottlenecks”, i.e., devices that have long service times for data accesses because of the quantity of requests they receive. System performance is generally improved when different file systems and databases that receive heavy concurrent use are stored on different storage devices within the system.
There are known techniques for improving storage system performance by selectively moving stored data within a system in a manner calculated to reduce the service times provided by devices within the system. In one such technique, statistical data is collected regarding the accesses to logical volumes stored on storage devices within a storage system. This statistical data is aggregated over many sample intervals to obtain a measure of average or total service time for each storage device within the system over an analysis interval that may span several days or longer. A pair of candidate storage devices and one or more pairs of potentially exchangeable logical volumes are then identified, and further processing is performed to determine whether the service times of the storage devices can be improved by exchanging the logical volumes of one or more of the pairs between the two drives, i.e., by moving each volume of the pair from its present storage device to the other storage device. In particular, it is determined whether the service time of a more heavily loaded storage device will be reduced, and the service time of a less heavily loaded storage device will not be increased unduly, if the exchange of logical volumes is performed. If so, the logical volumes are marked as a potential swap that can be performed in a subsequent swap operation. The above analysis is repeated for some number of the logical volumes of the storage system (which may be as many as all of them) to identify potential swaps that can be performed, and one or more of these swaps are carried out in subsequent swap operations. This process is repeated at periodic measurement intervals to enable the system to continuously adjust to changing workloads and other factors affecting the pattern of disk activity.
A technique which is similar to that described above is provided in U.S. Pat. No. 6,711,649 to Bachmat et al. entitled “Load Balancing on Disk Array Storage Device,” the teachings of which are hereby incorporated by reference in their entirety.